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So, I drain my tranny to replace the oil. Tranny and OD were working great, so a preventative fluid change should cover me for the season, right? I took the big plug off of the bottom of the OD because it was leaking and I was going to replace the gasket under the plug. These pieces (pics of front and back) came out with the oil. Ugh. So, I need to investigate. I figure it's the rear thrust washer so I order all possible thrust washers and o-rings in preparation.
So, I take the OD off and find that the problem isn't what I thought. It turns out that there's a top-hat bushing in the "pump housing" that isn't listed in any of the exploded diagrams or parts lists. It's broken.
Here's the broken bushing:
Here's the intact bushing in an old OD unit:
Posted links to the pictures to the FOT list. A couple of folks suggested that I talk to John at Quantum Mechanics. Excellent advice. John says that this is a top hat bushing and is only available used. He has them. Others mention that the Laycock manual says that bushing can't be replaced (and sends a PDF of that manual, posted at the end of this page). But, John says he's replaced it many times. It needs to be pressed into place and if that distorts the bushing you need to hone it out so the output shaft from the tranny fits. Others say that if THAT's broken, probably other stuff is. Good call. Here's what I found when I took it apart. Mind you, this OD unit worked GREAT at the last race!
By the way, I'm not mentioning names of those who gave me advice in order to protect personal information. I do really appreciate all of the great advice I got!
So, I take it further apart. Here's what I find:
Planetary gears: there's supposed to be a thrust washer between the center gear (sun gear) and the housing. I find one small piece of it in the center hole. You can see the piece sitting on top of the planetary gear carrier. Looks like it was running that way for a bit because the shape of the depression in the planetary gear carrier is worn into the teeth of the sun gear.
Annulus and unidirectional clutch: carrier for the rollers in the unidirectional clutch is in parts. The remaining bits of the thrust washer and some pieces of the carrier can be seen in this shot.
While I'm disassembling, the remainder of the top hat bushing comes out easily (was no longer pressed into the front housing). Here's the remains compared to a good bushing from the backside of the housing.
Hopefully the "spare" OD will be in better shape (it appears to have been rebuilt, based on disassembly so far) and I'll probably end up with many parts of that one in the car for the season.
Here's a link to the Laycock A-type overdrive manual:
Also, here are links to Larry and Sam's excellent guides to TR-4 tranny and A-type overdrive disassembly and reassembly: